This invention relates to microwave frequency circuits and more particularly to a phase shifter circuit for varying the phase of an applied signal.
As is known in the art a phase shifter is often employed, for example, in phased array antenna systems to control the phase of a microwave frequency signal used to generate a portion of a desired radiation pattern. One technique for realizing a phase shifter, the so called ferrite phase shifter, includes a bar of ferromagnetic material disposed coaxially within a section of waveguide. A solenoid is formed around the waveguide and when energized with an electric current produces a magnetic field. The magnetic field causes variations in the permability of the bar resulting in a variation in the propagation constant of the microwave frequency energy. The resulting variation in the propagation constant produces a phase shift of an applied microwave frequency signal. The ferrite phase shifter, in addition, requires driver circuits to control the electric current which produces the magnetic field. Another technique for realizing a phase shifter employs p-i-n diode switches. The switched line p-i-n diode phase shifter, includes two single pole double throw (SPDT) p-i-n diode switches for each bit and two line lengths coupled between each SPDT switch.
The prior art approaches, as exemplified above, in general employ passive techniques to provide the desired phase shift. These approaches have several disadvantages including: microwave frequency signal loss due to dissipation of the signal in the passive element of the phase shifter; and a relatively large switching power is required to switch the passive elements that provide the desired phase shift. Further, the above approaches, particularly the ferromagnetic approaches, have relatively long switching times, typically in the order of hundreds of microseconds. Such long switching times are undersirable for fast scanning of the array. Moreover, the above approaches are difficult to realize using monolithic microwave integrated circuit techniques.